The invention disclosed herein relates to an electrical digital display which incorporates some, but not all, of the moving (scrolling) digit features of a mechanical drum-type counter.
Electrical digital displays in which the digit values being displayed change instantaneously with changes in a parameter of an input signal are well known in the art. Such displays have the disadvantage of being unreadable when the input signal parameter being displayed changes rapidly, i.e., the digit values, particularly the least significant digit, change so quickly, or "wink", that the display is unreadable at an appropriate sampling rate. The display ma be made readable by decreasing the sampling rate, but that may result in inaccurate display readings. Another disadvantage of such displays is that they are incapable of indicating trends, in contrast to analog displays such as meters and mechanical drum-type counters.
U.S. Pat. Nos. 3,132,338 (Schmid) and 3,714,569 (Bruning, Jr. et al.) disclose electrical displays which include a digital display portion and an analog display portion. The least significant digit is displayed in the analog display portion and the more significant digits in the digital display portion. The analog display portion of those displays comprises a conventional, e.q., moving-coil, meter and the digital display portion comprises gas discharge. e.g. Nixie, tubes. The analog portion includes a pointer or scale which moves with input signal parameter change rather than changing instantaneously, and the more significant digits in the digital portion of the display change instantaneously when the least significant digit changes between its highest and lowest values. Thus, display of the least significant digit does not wink and the display is capable of indicating trends.
U.S. Pat. No. 3,914,758 (Ingle) discloses a display which is capable of indicating trends in the least significant digit and which utilizes gas discharge tubes for displaying each of the digits of the input signal parameter. Two gas discharge tubes digitally display the more significant digits conventionally, i.e., they change the displayed value instantaneously when the adjacent less significant digit changes between its highest and lowest values. Although the least significant digit is also displayed by a gas discharge tube, it is not displayed as a number or digit. Instead, selected elements of the least significant digit gas discharge tube are illuminated in accordance with a code to represent the instantaneous value of the least significant digit. In addition, the intensity of illumination of the selected elements is proportional to the time that the least significant digit has the value represented by the illuminated element(s). Thus, a visual indication of trends in the value of the least significant digit is represented by the relative brightness of the individual elements of the least significant digit gas discharge tube. However, one must know the code to be able to read the value of least significant digit.
While those displays at least partly avoided the winking disadvantage of fully digital electric displays and were capable of indicating trends, they are not suitable for certain applications such as aircraft instruments.
U.S. Pat. No. 3,383,594 (Fiorletta et al.) discloses a cathode ray tube (CRT) display of a single digit in which the single displayed digit is scrolled with input signal variable change. That display also is capable of indicating trends in changes of the input signal variable.
Electrical digital displays which duplicate features of mechanical drum-type counters using electrical and electrooptical components are disclosed, for example, in U.S. Pat. Nos. 4,570,151 (Martorano et al.), 4,240,074 (Gibson et al.), and 4,581,612 (Jones). In the displays disclosed in those Patents, display of the least significant digit is displaced or scrolled in accordance with changes in the input signal parameter. In addition to scrolling the least significant digit, the displays of those Patents also scroll a more significant digit in synchronism with an adjacent less significant digit when the adjacent less significant digit changes between its highest and lowest values. Such displays are intended to fully duplicate the display features of mechanical drum-type counters and may be used as aircraft instruments and automobile odometers. However, in duplicating the moving digit features of mechanical counters, they also incorporate certain disadvantages of mechanical counters.
One disadvantage of mechanical drum-type counters and their electrical counterparts is that they are unreadable at certain transition points where a number of the digits is changing. For example, in a four digit counter or display, the transition between 1999 and 2000 at approximately 1999.5 is unreadable. Another disadvantage of such counters and displays is that the least significant digit is frequently not readable when it is at a transition point and not aligned with the more significant digits. A display including scrolling of the least significant digit combined with instantaneous changing of the more significant digits, as taught, for example, by combining the Fiorletta et al., Schmid, Bruning, Jr. et al. and Ingle Patents, would eliminate the one disadvantage referred to above but not the other.
U.S. Pat. Nos. 3,275,871 (Yiotis), 4,155,084 (Klees) and 4,232,312 (Eccles et al.) disclose electrical displays which indicate an input signal parameter value in analog form, for example, as a pointer or bar graph. U.S. Pat. Nos. 3,343,155 (Pahlavon), 3,460,127 (Pahlavon), and 3,594,757 (Gard) disclose electrical displays duplicating mechanical moving tape indicators. U.S. Pat. No. 4,176,546 (Gibson et al.) discloses a mechanical display having a meter portion and a drum-type counter portion which provide both a digital and an analog readout of an input signal parameter.
The electrical display and method of displaying disclosed herein overcome the disadvantages described above of mechanical drum-type counters and their electrical counterparts, as well as other disadvantages of mechanical counters.